"If a fox or a turtle survived their first century, they would absorb enough vital aura from the world around them to ascend into sacred beasts. These animals cycled madra, advanced in power, and left Remnants just as humans did. The oldest of them could even speak, and legends said some could take human forms." ― Will Wight, Unsouled pg7[source]
`Sacred Beasts are animals on cradle that have attained sacred status by absorbing enough vital aura from their surroundings to advance in the sacred arts. Sacred differ from human sacred artists in the way they advance, though the specifics on how they differ is not yet well known.